Unsaturated polyester resin compositions and electrical laminates made therefrom

ABSTRACT

An unsaturated polyester composition is provided comprising an unsaturate polyester component, a cross-linking monomer and as a modifier of the resin a polyoxyalkylene alcohol at least partially esterified with a polymerizable unsaturated carboxylic acid. The modifier is produced by esterifying the hydroxy group of a polyoxyalkylene mono- or polyalcohol at least partially with a polymerizable carboxylic acid such as a maleic acid.

This is a divisional application of Ser. No. 07/296,159, filed Jan. 12,1989 now U.S. Pat. No. 4,943,474.

BACKGROUND OF THE INVENTION

This invention relates to an unsaturated polyester resin compositionwhich is particularly useful in the manufacture of electrical laminates.The term "electrical laminates" as used herein refers to uncladinsulation boards for mounting various electrical and electronic partsthereon as well as one or both sided metal clad laminates for use in themanufacture of printed circuit boards (PCBs). They are normally in theform of a flat sheet having a thickness of about 0.5-5 mm.

Electrical laminates made from unsaturated polyester resins are nowcommercially available and consumed in large quantities. These laminatesare produced by ore treating a cellulosic substrate with a melamine typeresin, impregnating the substrate with a liquid unsaturated polyesterresin, laminating a plurality of the resin-impregnated substrates, andcuring the laminate. A continuous process for the production thereof isdisclosed in U.S. Pat. No. 4,372,800 assigned to the assignee of thisapplication.

Unsaturated polyester resins in general find a variety of uses owing totheir excellent mechanical properties and molding workability withvarious reinforcing materials. For use in the manufacture of PCBs, theymust comply with high standard requirements for properties in terms ofpunching property, solder dip resistance, impact strength and the like.Needs exist for resins having an improved impact strength withoutdeteriorating heat resistance in the field of large FRP products. Theseproperty requirements have become more stringent as automated processingof PCBs has become more popular and parts are packaged thereon moredensely. However, these requirements are often incompatible. Forexample, it has been difficult to improve both the heat resistance andimpact strength simultaneously or to improve all of the low temperaturepunchability, solder dip resistance and impact strength while keeping agood balance among them.

Attempts have been made to improve the impact strength by modifyingunsaturated polyester resins with flexible resins, plasticizers, liquidbutadiene-based polymers, cross-linked diene- or acrylic based rubbersand the like. However, the incorporation of these modifiers is notsatisfactory in that they tend to deteriorate heat resistance, chemicalresistance, stability against phase separation, substrate-impregnatingproperties and other properties.

It is, therefore, a major object of the present invention to overcomethe above discussed problems. Other objects and advantages thereof willbecome apparent as the description proceeds.

SUMMARY OF THE INVENTION

These and other objects and advantages are achieved, in accordance withthe present invention, by providing an unsaturated polyester resincomposition comprising an unsaturated polyester component, across-linking monomer and a polyoxyalkylene alcohol at least partiallyesterified with a polymerizable unsaturated carboxylic acid.

In a preferred embodiment of the present invention, said unsaturatedpolyester component is a mixture of a hard unsaturated polyester and asoft unsaturated polyester, said soft polyester containing apolyoxyalkylene segment having a molecular weight from 600 to 6000 inthe backbone thereof, said hard polyester being free from saidpolyoxyalkylene segment.

The present invention also provides an electrical laminate comprising aplurality of layers of a fibrous substrate impregnated with theunsaturated polyester resin composition of the present invention.

Electrical laminates produced from the resin composition of the presentinvention exhibit improved impact strength and low-temperaturepunchability without deteriorating heat resistance and other properties.

DETAILED DISCUSSION

As is well-known, unsaturated polyesters are polycondensates of an α,β-ethylenically unsaturated polycarboxylic acid optionally containing anunsaturated monocarboxylic acid and/or a polycarboxylic acid free fromethylenic unsaturation with a polyhydric alcohol optionally containing amonoalcohol. Unsaturated polyester resins are mixtures of theunsaturated polyester and a cross-linking monomer, typically styrene.

The unsaturated polyester composition of the present inventionadditionally contains, as a modifier of the unsaturated polyester resin,a partially esterified product of a hydroxy-terminated polyoxyalkylenecompound.

Although any conventional unsaturated polyester resin may be modified bythe present invention, an unsaturated polyester resin formulationcontaining a hard unsaturated polyester and a soft unsaturated polyesteras disclosed in U.S. Pat. No. 4,710,420 assigned to the assignee of thisapplication is preferable. The entire disclosure of said patent isincorporated herein by reference. The soft polyester component containsa polyoxyalkylene segment having a molecular weight from 600 to 6000 inthe backbone thereof, while the hard polyester component is free fromsaid polyoxyalkylene segment.

The hard polyester component may be prepared by reacting an unsaturatedpolycarboxylic acid, acid anhydride or mixtures thereof optionallycontaining an unsaturated monocarboxylic acid and/or a satutatedpolycarboxylic acid with a polyhydric alcohol optionally containing amono alcohol.

Examples of unsaturated polycarboxylic acids and acid anhydrides includemaleic anhydride and fumaric acid. The term "unsaturated" as used hereinmeans an ethylenic unsaturation present between alpha and beta positionsrelative to the carboxyl group. Maleic acid dicyclopentadiene monoester(DCPD monomaleate) is an example of unsaturated monocarbocylic acid.Examples of saturated polycarboxylic acid include phthalic acid,isophthalic acid, terephthalic acid, tetrahydrophthalic acid, endicacid, trimellitic acid, pyromellitic acid, tetrabromophthalic acid,dibromoterephthalic acid, chlorendic acid, adipic acid, succinic acid,azelaic acid, sebacic acid and acid anhydrides of these acids. The term"saturated" as used herein means the absence of an ethylenicunsaturation between alpha and beta positions relative to the carboxylgroup. It is desirable that the sum of unsaturated polycarboxylic acidand unsaturated monocarboxylic acid occupy from 40 to 100 mole % of thetotal acid reactants.

Examples of polyhydric alcohols includes ethylene glycol, propyleneglycol, butanediol, neopentyl glycol, diethylene glycol, dipropyleneglycol, hexanediol, hydrogenated bisphenol A, glycerine,trimethylolpropane, pentaerythritol, dibromoneopentyl glycol, adducts ofethylene oxide or propylene oxide with bisphenol A, adducts of ethyleneoxide or propylene oxide with tetrabromobisphenol A and bisphenol Aepoxide. Examples of monoalcohols include hydroxylateddicyclopentadiene, ethylene glycol monomethyl ether, cinnamyl alcoholand stearyl alcohol.

For use in the manufacture of electrical laminates, the hard polyestercomponent may preferably be flame retarded. This may be effected bysynthesizing the polyester using halogen-containing acid or alcoholcomponents such as dibromophthalic acid, chlorendic acid,dibromoneopentyl glycol or adducts of ethylene oxide or propylene oxidewith tetrabromobisphenol A. Alternatively an unsaturated polyester maybe synthesized using as a part of acid and/or alcohol reactants acompound having a double bond to which a halogen molecule maypreferentially be added. Thereafter the resulting polyester may bepost-halogenated without halogenating ethylenic alpha, betaunsaturation. Examples of such acid and alcohol reactants include DCPDmonomaleate, tetrahydrophthalic acid, hydroxylated DCPD and cinnamylalcohol. In a preferred embodiment, the hard polyester component isprepared by post-brominating an unsaturated polyester including atetrahydrophthalic acid moiety in the middle of the polymer chain- and aDCPD monomaleate moiety at each terminal of the polymer chain.

The soft polyester component used in the present invention may beprepared in the same way as the hard polyester component as discussedabove except that the soft polyester component additionally contains anpolyoxyalkylene segment having a molecular weight from 600 to 6000 inthe backbone thereof. The incorporation of polyoxyalkylene segment maybe effected by using as a part of alcohol reactants a polyoxyalkylenemonoalcohol and/or a polyoxyalkylene polyol having a molecular weight of600 to 6000, or by copolymerizing said polyoxyalkylene mono- and/orpolyalcohol with an oligomer of unsaturated polyester free from thepolyoxyalkylene segment. The polyoxyalkylene chain content of the softpolyester may range from 25 to 75%, preferably from 25 to 50%, morepreferably from 25 to 40% by weight. Examples of polyoxyalkylene chainsinclude homopolymers of propylene oxide, copolymers of propylene oxideand ethylene oxide, copolymers of propylene oxide and tetramethyleneoxide and copolymers of ethylene oxide and tetramethylene oxide.Polyoxypropylene mono- or polyalcohols are preferable. Preferably thesoft polyester component also has a DCPD monomaleate moiety at eachterminal. This increases its compatibility with the hard unsaturatedpolyester component and decreases the moisture absorption of the entirecomposition. The soft polyester component may or may not bepost-haloganated for rendering flame retardant.

The modifier ester may be synthesized by esterifying polyoxyalkylenemono or polyalcohols with a polymerizable unsaturated carboxylic acid bythe conventional method. The term "at least partially esterified" refersto about 20 to 80 mole %, preferably about 40 to 70 mole % of thehydroxy group possessed by the polyoxyalkylene polyols, and about 40 to100 mole %, preferably about 80 to 100 mole % of the hydroxy grouppossessed by the polyoxyalkylene monoalcohols are esterified with thepolymerizable unsaturated carboxylic acid. Within these ranges of degreeof esterification, the polyoxyalkylene ester exhibits a goodcompatibility with other components and the entire composition exhibitsa reduced moisture absorption.

Examples of polyoxyalkylene alcohols include diols such as polyethyleneglycols, polypropylene glycols, ethylene oxide-propylene oxide block orrandom copolymers; polyols having corresponding polyoxyalkylene chainsderived from polyols such as glycerine, trimethylolpropane,pentaerythritol and the like, and monoethers and monoesters of the abovepolyoxyalkylene diols. The polyoxyalkylene alcohols preferably have anaverage molecular weight from 2000 to 8000. Examples of polymerizableunsaturated carboxylic acids includes acrylic acid, methacrylic acid,crotonic acid, fumaric acid, maleic acid and maleic anhydride. Maleicanhydride is preferable. The reaction of maleic anhydride with thepolyoxyalkylene alcohol may be carried out at a temperature from 60° C.to 170° C., preferably from 100° C. to 150° C. under normal or elevatedpressures. The completion of the esterification reaction may bedetermined by the acid number or viscosity of the reaction mixture. Thereaction is preferably carried out under pressure for promoting thereaction and also for preventing sublimination of maleic anhydride. Careshould be taken, however, that the reaction temperature does not exceed170° C. at which a polycondensation reaction begins to take place. Themodifier ester is added in an amount of 2 to 10% by weight of thecomposition.

Examples of cross-linking monomers include styrene, α-methylstyrene,vinyltoluene, p-methylstyrene, chlorostyrene, divinylbenzene, C₁₋₁₀alkyl acrylates, C₁₋₁₀ alkyl methacrylate, hydroxyalkyl acrylates,hydroxyalkyl methacrylates, diallyl phthalate, triallyl cyanurate andmixtures of these monomers. Styrene is most preferable. The proportionof cross-linking monomer ranges between 10 and 70%, preferably 20 and50% based on the combined weight of the hard polyester, the softpolyester, the modifier ester and the cross-linking monomer.

The proportions of the soft polyester component and the modifier esterin the entire resin composition are such that the total polyoxyalkylenechain content ranges from 5 to 30%, preferably from 6 to 25%, morepreferably from 8 to 20% based on the combined weight of the hardpolyester, the soft polyester, the modifier and the cross-linkingmonomer.

The unsaturated resin composition of the present invention may containconventional additives such as additive type flame retardants, fillers,antioxidants, stabilizers, other polymers, colorants and the like asdesired. Examples of additive type flame retardants include phosphorusbased flame retardants such as trioctyl phosphate, triphenyl phosphate,tricresyl phosphate, triethyl phosphite, triphenyl phosphite,tris-(chloroethyl)phosphate and red phosphorus; halogenated flameretardants such as chlorinated paraffin, tetrabromobisphenol A and itsderivatives, and tribormophenyl monoglycidyl ether; antimony compoundssuch as antimony tri-or pentoxide and sodium antimonate; and other flameretardants such as zinc borate and aluminum hydroxide.

In order to promote the compatibity of the modifier component with othercomponents, a small amount of substances such as polycaprolactone,saturated polyesters, vegetable oil derivatives, dimer acid derivatives,xylene resins and mixtures of these substances may be added.

The resin composition of the present invention may be cured using anyconventional peroxide catalyst. Examples of preferred peroxide catalystsinclude peroxy ketals such as 1,1-bis-(t-butylperoxY)-3,3,5-trimethylcyclohexane and 1,1-bis-(t-butylperoxy)cyclohexane; anddialkyl peroxides such as di-t-butylperoxide; and peroxyesters such ast-butylperoxy benzoate. These catalysts may be incorporated in amountsfrom 0.5 to 2.0 parts per 100 parts by weight of the resin composition.The resin composition may also be cured by irradiating with actinicradiation such as UV radiation, electron beam radiation and otherradiation as desired by incorporating an appropriate curing catalyst.

The unsaturated resin composition of the present invention is highlysuited for, but not limited to, the production of electrical laminates.In such use, a fibrous substrate or reinforcement is impregnated withthe resin composition of the present invention. A plurality ofresin-impregnated substrates are combined together optionally with acladding metal foil being placed on one or both sides and the resultinglaminate is cured. The entire operation may preferably be carried out ina continuous mode as described in the hereinbefore cited U.S. Pat. No.4,372,800. Examples of substrates include glass substrates in the formof cloth, mat or paper; and cellulosic substrates such as kraft paper,or cotton linter paper. Cellulosic substrates pretreated with aminoplastresin are preferable.

The following examples will illustrate the present invention. All partsand percents therein are by weight unless oterwise indicated.

EXAMPLE Soft unsaturated polyester resin (A)

A one liter flask equipped with stirrer, thermometer, nitrogengas-introducing tube, and distillation column was charged with 69.5 g ofDCPD monomaleate, 165.8 g of bis(propyleneglycol)isophthalate, 136.4 gof bis(propyleneglycol)fumarate, 168 g of polypropylene glycol(averageM.W.=1200) and 82.4 g of maleic anhydride. The reaction was continuedunder nitrogen gas stream at an inner temperature of 150°-200° C. untilan acid number of 20 was reached. The reaction product was allowed tocool. When the temperature was dropped to 160° C., 90 mg of hydroquinonewas added. When the temperature was dropped to 100° C., an amount ofstyrene was added to a styrene content of 35%.

Hard unsaturated polyester resin (B)

A similar one liter flask was charged with 198.6 g of DCPD monomaleate,236 g of bis(propyleneglycol)fumarate, and 39.2 g of maleic anhydride.The reaction was continued at an inner temperature of 150°-200° C.,until an acid number of 20 was reached. The reaction product was allowedcool. When the temperature was dropped to 160° C., 90 mg of hydroquinonewas added. When the temperature was dropped to 100° C., an amount ofstyrene wad added to a styrene content of 35%.

Modifier ester (C)

A one liter flask equipped with stirrer, thermometer and nitrogen gasintroducing tube was charged with 700 g of a tri-functionalpolyoxyalkylene polyol having an average M.W. of 3500 (EP530, MITSUINISSO POLYURETHANE CO., LTD.) and 29.4 g of maleic anhydride. Thereaction was continued at an inner temperature of 100°-150° C., for 6hours until an acid number of 24.3 was reached.

Production of copper clad laminate

50 parts of soft polyester resin (A), 50 parts of hard polyester (B), 5parts of modifier (C) and 1 part of BPO (benzoyl peroxide) werethoroughly mixed to prepare an impregnating liquid resin.

A kraft paper having a thickness of 285 microns was pretreated with amethanolic solution of methylolmelamine and then dried. This papersubstrate was impregnated with the above liquid resin. Five plies of theresin impregnated substrates and a 35 micron thickness copper foilhaving a coating of epoxy adhesive were laminated. The laminate wascured at 100° C. for 30 minutes to give a one sided copper clad laminatehaving a thickness of 1.6 mm. Properties of the laminate are shown inTable 1.

COMPARATIVE EXAMPLE 1

A one sided copper clad laminate having a thickness of 1.6 mm wasproduced as the laminate of Example using a resin composition consistingof 50 parts of soft polyester resin (A), 50 parts of hard polyesterresin (B) and 1 part of BPO. Properties of the laminate are shown inTable 1.

COMPARATIVE EXAMPLE 2

A one sided copper clad laminate having a thickness of 1.6 mm wasproduced as the laminate of Example using a resin composition consistingof 50 parts of soft polyester resin (A), 50 parts of hard polyesterresin (B), 5 parts of unesterified polyoxyalkylene polyol EP530 and 1part of BPO. Properties of the laminate are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                                     Compara-                                                                              Compara-                                 Test item  Unit     Example  tive Ex.1                                                                             tive Ex.2                                ______________________________________                                        Flexural modulus                                                                         kg/mm.sup.2                                                                            300      300     290                                      at 100° C. (a)                                                         Drop ball impact                                                                         cm        30       22      30                                      strength (b)                                                                  Low temperatur      Good     Not good                                                                              Good                                     punchability (c)                                                              Solvent resistance  Good     Good    Not good                                 (d)                                                                           ______________________________________                                         (a) JIS C6481                                                                 (b) A dropping height of a steel ball weighing 55 g to cause 50% fracture     of the laminate.                                                              (c) A punching die having a series of ten pins having a diameter of 0.8 m     arranged at an interval of 1.78 mm was used at 25° C. Evaluation       was made based on the degree of delamination.                                 (d) Boiling in trichloroethylene for 10 minutes. Evaluation was made base     on the change in appearance.                                             

As can been seen from Table 1, the laminate of Example exhibitedexcellent impact strength and low temperature-punchability whencomparing with the laminate of Comparative Example 1 which is free fromthe modifier (C). It also exhibited excellent solvent resistance whencomparing with the laminate of Comparative Example 2 which contains afree polyoxyalkylene polyol corresponding to the modifier (C).

We claim:
 1. An unsaturated polyester resin composition comprising (a) amixture of a hard unsaturated polyester and a soft unsaturatedpolyester, said soft polyester containing a polyoxyalkylene segmenthaving a molecular weight from 600 to 6000 in the backbone thereof, saidhard polyester being free from said polyoxyalkylene segment, (b) acrosslinking monomer, and (c) a polyoxyalkylene polyol having an averagemolecular weight from 2000 to 8000 and about 20 to 70 mole % of whosehydroxy groups are esterified with a polymerizable unsaturatedcarboxylic acid.
 2. The composition according to claim 1, wherein saidpolymerizable unsaturated carboxylic acid is maleic acid.
 3. Thecomposition according to claim 1, wherein said polyoxyalkylene alcohol(c) is present in an amount from 2 to 10% by weight of the sum of saidhard soft polyester, said soft polyester, said crosslinking monomer andsaid polyoxyalkylene alcohol ester.
 4. The composition according toclaim 1, wherein said soft polyester contains from 25 to 75% by weightof said polyoxyalkylene segment.
 5. The composition according to claim1, wherein the proportions of said soft polyester and saidpolyoxyalkylene alcohol therein are such that the total polyoxyalkylenecontent of said composition is from 5 to 30% by weight of the sum ofsaid hard polyester, said soft polyester, said crosslinking monomer andsaid polyoxyalkylene alcohol ester.
 6. The composition according toclaim 1, wherein said composition contains said crosslinking monomer inan amount from 10 to 70% by weight of the sum of the hard polyester, thesoft polyester, said crosslinking monomer and said polyoxyalkylenealcohol.
 7. The composition according to claim 1, wherein said hardpolyester is post-halogenated.
 8. An electrical laminate comprising aplurality of layers of fibrous substrate impregnated with the resincomposition of claim
 1. 9. An electrical laminate comprising a pluralityof layers of a fibrous substrate impregnated with the resin compositionof claim
 2. 10. An electrical laminate comprising a plurality of layersof a fibrous substrate impregnated with the resin composition of claim3.
 11. An electrical laminate comprising a plurality of layers of afibrous substrate impregnated with the resin composition of claim
 4. 12.An electrical laminate comprising a plurality of layers of a fibroussubstrate impregnated with the resin composition of claim
 5. 13. Anelectrical laminate comprising a plurality of layers of a fibroussubstrate impregnated with the resin composition of claim
 6. 14. Anelectrical laminate comprising a plurality of layers of a fibroussubstrate impregnated with the resin composition of claim 7.